Fighting among the leadership may threaten Viacom's ability to improve its fiscal performance, S&P Global Ratings said Tuesday as it revised its ratings outlook to negative.

The ongoing dispute between Viacom's board and management could "adversely affect" the media company's financial turnaround, S&P Global Ratings said in a statement Tuesday, though it affirmed Viacom's BBB- corporate credit rating. The negative revision, down from stable, reflects increased doubts that Viacom can maintain its leverage threshold until September 2017, the statement said.